Blade cluster having an offset axial mounting base

ABSTRACT

The stage of a turbine or of a compressor having a plurality of blades which are mounted on a rotor and/or a stator of the stage. The blades are combined into a number of blade clusters as integral components which are each composed of at least two blades and which are each equipped with one shared blade mount for mounting the cluster on the rotor or stator.

The present invention relates to a blade.

BACKGROUND

Turbine stages, which are built for turbines that are subject to relatively high loads, and also compressor stages are generally equipped with individual blades that are each hooked via a profiled root into a disk having grooves and are fixed in position therein.

The related art in accordance with the German Patent Application DE 198 58 702 A1, for example, describes the blade of a turbine machine that is mounted on a rotor or stator via an axially oriented dovetail root in the form of a fir tree. For this, the disk-shaped rotor in the form of a disk, has a number of axially extending grooves on its radial peripheral surface which, in the aforementioned form, form a plurality of radially spaced apart undercuts in the direction of the groove base. Accordingly, the root is composed of a fir tree-shaped projection, on which a number of peripherally extending undercuts are formed in such a way that the root can be inserted into the groove in the axial direction of the rotor and fixed in position therein.

An exceptionally high transfer of force is, in fact, made possible by a connection of this kind. However, the usefulness of a compressor or turbine stage constructed in this manner for the aviation sector is substantially limited by its weight. In particular, under the latest state of the art, high-speed LPTs (low-pressure turbines) are still characterized by an exceedance of the predefined optimal weight, thereby necessitating an optimal design of the rotor components, in particular.

The rotors of compressor and turbine stages that are built in accordance with the BLISK design principle offer one approach for partially resolving the aforementioned problem. The basis for a BLISK is preferably a forged disk, out of whose outer contour, the blade profiles are machined, for example. This means that the disk and the blades are fabricated from one part.

The assembly costs for the blades are eliminated by replacing sometimes more than 120 individual blades per disk with such a BLISK, thereby altogether reducing the outlay required for manufacturing a new component. Moreover, by employing this method, it is possible to achieve a substantial weight reduction which is of considerable importance in aviation, in particular. For the most part, however, at the present time, only engine components that are relatively less stressed are able to be replaced by a BLISK that is manufactured in accordance with the above mentioned method. Also, refurbishing a BLISK is a very complex and expensive process in comparison to replacing individual blades.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a blade mount that will make possible a lightest possible design and that will, nevertheless, be able to withstand high loads.

In accordance with the present invention, blade clusters are integral components composed of at least two blades that are equipped with one (single) shared blade mount for mounting the cluster on the rotor or stator.

An especially high force transmission is ensured in that the blade mount is designed as an axially extending dovetail connection having at least one undercut (on each lateral face). This type of connection may be produced with high precision and assembled inexpensively.

The dovetail connection is advantageously configured in a decentralized location between the blades, preferably offset circumferentially. This allows the loads acting on the blades to be introduced to each dovetail contact surface as distributed loads, instead of as centrally consolidated loads, thereby reducing the high stress concentration loads that form in the process. This makes it possible for the dovetail connection to have a less massive design, respectively for it to transmit higher forces. In this context, with respect to the introduction of force, it proves to be especially beneficial when the circumferential offset is equal to approximately one half of a blade pitch.

It is also preferable that the groove, respectively the recess of the dovetail connection be formed on the side of the blade cluster, and that the root, respectively the projection be formed on the side of the rotor or stator. This reduces the weight of the cluster and thus the force load of the connection.

Other advantageous embodiments of the present invention constitute the subject matter of the remaining dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is clarified in greater detail in the following on the basis of a preferred exemplary embodiment and with reference to the accompanying drawings.

FIG. 1: shows the radially outer circumferential portion of a turbine or compressor disk having the blade cluster mounted thereon in accordance with one preferred exemplary embodiment of the present invention;

FIG. 2: shows the blade cluster in the uninstalled state;

FIG. 3: shows an alternate embodiment of the blade cluster; and

FIG. 4: shows an alternate embodiment of the dovetail joint of FIG. 2.

DETAILED DESCRIPTION

In accordance with FIGS. 1 and 2, a blade cluster 1 of a turbine or compressor stage is composed of a pair of blades 2 which, at the radially inner ends thereof, are joined to a shared blade root 3. The radially outer ends are coupled to one another via a flat band 4 (referred to by experts as a “plain shroud”). Blade cluster 1 having the preceding components is formed in an integral type of construction, for example by friction welding or inductive high-frequency pressure welding, and also preferably in one piece.

As is inferable from FIG. 2, in particular, blade root 3 is composed of a root plate 5, to whose radial upper side the two radially inner blade ends are attached and on whose radial bottom side a root base 6 is formed in such a way that root plate 5 has a strip-shaped overhang relative to base 6. Machined into this root base 6 in the present case is a groove 7, which extends right through in the axial direction of the stage relative to the row of blades. Groove 7 is produced in the form of a dovetail and thus forms an undercut at each groove side.

As is also illustrated in FIG. 2, groove 7 is not centrally located in the middle between the two blades 2, respectively the inner blade ends thereof, but rather, in the present case, is configured so as to be offset by approximately one half of a blade pitch in the circumferential direction, namely in accordance with FIG. 1, in the direction of the action of force of blades 2.

FIG. 1 shows a portion of a disk (rotor) 8 of the stage. Accordingly, disk 8 is axially widened at the radially outer periphery thereof to form what is generally known as a fillet interface 9, on whose radial outer side, a number of tongue-type strips 10 are formed in one piece with disk 8 in the axial direction of the stage. Tongues 10 are spaced uniformly apart in the circumferential direction.

Moreover, in cross section, tongues 10 form a dovetail shape and thus form the mating component to grooves 7 on the side of blade cluster 1. Grooves 7 and tongues 10 are dimensioned in such a way that a press-fit connection is formed when they are joined together.

To assemble blade cluster 1 and disk 8, blade roots 3 are slid onto disk-side tongues 10 in the axial direction until a burr-free transition is formed between disk 8 and root 3. In this manner, individual blade clusters 1 are assembled to form a complete blade ring.

At this point, it should be noted that a blade cluster 1 may also have more than two blades, for example three blades, as shown in FIG. 3 with blades 2 a, 2 b, 2 c on base 6. Also, blade root 3 is not limited to a simple dovetail shape. As is also known from the related art, it may be designed in the shape of a fir tree having a plurality of undercut edges per side face, as shown in FIG. 4 with groove 7 a in base 6 a. Finally, it is not absolutely necessary that groove 7 be designed to be through-extending. Rather, it may be closed on one side, thereby forming a predefined limit stop for mounting blade cluster 1. 

1-8. (canceled)
 9. A stage of a turbine or of a compressor comprising: a rotor or stator; blades mounted on the rotor or stator, the blades being combined into a number of blade clusters as integral components each composed of at least two blades, each blade cluster equipped with one shared blade mount for mounting the blade cluster on the rotor or stator.
 10. The stage as recited in claim 9 wherein the blade mount includes an axially extending dovetail groove or tongue for connection to a corresponding dovetail tongue or groove, respectively, on the rotor or stator.
 11. The stage as recited in claim 10 wherein the dovetail connection is configured in a decentralized location between the at least two blades.
 12. The stage as recited in claim 11 wherein the dovetail connection is offset circumferentially from a central location between the at least two blades.
 13. The stage as recited in claim 12 wherein the circumferential offset is equal to approximately one half of a blade pitch, the direction of the offset corresponding to the direction of the action of force of the blades.
 14. The stage as recited in claim 9 wherein the blade mount is the dovetail groove formed on the blade cluster, and the corresponding tongue is formed on the rotor or stator.
 15. The stage as recited in claim 8 wherein each blade cluster has three blades.
 16. The stage as recited in claim 14 wherein the corresponding tongues are formed in one piece with the rotor or the stator.
 17. The stage as recited in claim 9 wherein the dovetail groove has the form of a fir tree and forms a plurality of radially spaced apart undercuts for each lateral face. 